Inhibition of FOXD1 gene expression increases radiosensitivity of colorectal cancer HCT116 cells

Abstract

Objective To study the effect of inhibiting the expression of FOXD1 gene on the radiosensitivity of colorectal cancer cells. Methods The expressions of FOXD1 mRNA and protein in human colorectal cancer tissues and cells were detected by Real-time PCR (qRT-PCR) and Western blot. The colorectal cancer cell line HCT116 was irradiated with 0, 2, 4 and 6 Gy of X-rays. The expression of FOXD1 in each groups were detected by qRT-PCR and Western blot. HCT116 cells were transfected with FOXD1 siRNA and its negative control and termed as si-FOXD1 group and si-NC group. When these cells were irradiated with 4 Gy X-rays, they were termed as si-FOXD1+ 4 Gy group and si-NC+ 4 Gy group. Cell proliferation was detected with MTT method, cell survival fraction was measured with colony formation assay, and DNA-PK activity was detected by TECT DNA-PK kit. The siRNA-transfected colorectal cancer cells were inoculated into BALB/c nude mice to establish the xenograft model. After irradiation, the volume and quality of the subcutaneous transplanted tumors were measured every 5 days. Results The expression of FOXD1 mRNA and protein in colorectal cancer tissues was higher than that in adjacent normal tissues (t=5.579, 4.816, P<0.05). The mRNA(t=5.85-17.62, P<0.05)and protein(t=9.04-11.42, P<0.05)expression of FOXD1 in different colorectal cancer cell lines was higher than that in colonic mucosa epithelial cell line NCM460. The expression of FOXD1 in colorectal cancer cells HCT116 was increased after radiation in a dose dependent manner(t=9.13-44.15, P<0.05). Transfection of si-FOXD1 effectively inhibited the expression of FOXD1 (t=10.51, P<0.05), decreased proliferation (t=10.41, P<0.05), increased radiosensitivity with a radiosensitization ratio of 1.797, and reduced the radiation-induced DNA-PK activity (t=6.20, P<0.05) in colorectal cancer cells. After localized irradiation, the tumor volume and weight in nude mice transplanted with si-FOXD1 HCT116 cells were significantly smaller than those in HCT116 (t=11.29, 3.69, P<0.05). Conclusions Knock-down of FOXD1 gene increases the radiosensitivity of colorectal cancer cells and inhibits the growth of colorectal cancer xenograft in nude mice, which provides a potential target gene in improving the effect of radiotherapy on colorectal cancer. Key words: FOXD1 gene; Colorectal cancer; Radiosensitiviy